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| <h3 class="section">7.8 Bundle directives</h3> |
| |
| <h4 class="subsection">7.8.1 <code>.bundle_align_mode </code><var>abs-expr</var></h4> |
| |
| <p><a name="index-g_t_0040code_007bbundle_005falign_005fmode_007d-directive-292"></a><a name="index-bundle-293"></a><a name="index-instruction-bundle-294"></a><a name="index-aligned-instruction-bundle-295"></a><code>.bundle_align_mode</code> enables or disables <dfn>aligned instruction |
| bundle</dfn> mode. In this mode, sequences of adjacent instructions are grouped |
| into fixed-sized <dfn>bundles</dfn>. If the argument is zero, this mode is |
| disabled (which is the default state). If the argument it not zero, it |
| gives the size of an instruction bundle as a power of two (as for the |
| <code>.p2align</code> directive, see <a href="P2align.html#P2align">P2align</a>). |
| |
| <p>For some targets, it's an ABI requirement that no instruction may span a |
| certain aligned boundary. A <dfn>bundle</dfn> is simply a sequence of |
| instructions that starts on an aligned boundary. For example, if |
| <var>abs-expr</var> is <code>5</code> then the bundle size is 32, so each aligned |
| chunk of 32 bytes is a bundle. When aligned instruction bundle mode is in |
| effect, no single instruction may span a boundary between bundles. If an |
| instruction would start too close to the end of a bundle for the length of |
| that particular instruction to fit within the bundle, then the space at the |
| end of that bundle is filled with no-op instructions so the instruction |
| starts in the next bundle. As a corollary, it's an error if any single |
| instruction's encoding is longer than the bundle size. |
| |
| <h4 class="subsection">7.8.2 <code>.bundle_lock</code> and <code>.bundle_unlock</code></h4> |
| |
| <p><a name="index-g_t_0040code_007bbundle_005flock_007d-directive-296"></a><a name="index-g_t_0040code_007bbundle_005funlock_007d-directive-297"></a>The <code>.bundle_lock</code> and directive <code>.bundle_unlock</code> directives |
| allow explicit control over instruction bundle padding. These directives |
| are only valid when <code>.bundle_align_mode</code> has been used to enable |
| aligned instruction bundle mode. It's an error if they appear when |
| <code>.bundle_align_mode</code> has not been used at all, or when the last |
| directive was <code>.bundle_align_mode 0</code><!-- /@w -->. |
| |
| <p><a name="index-bundle_002dlocked-298"></a>For some targets, it's an ABI requirement that certain instructions may |
| appear only as part of specified permissible sequences of multiple |
| instructions, all within the same bundle. A pair of <code>.bundle_lock</code> |
| and <code>.bundle_unlock</code> directives define a <dfn>bundle-locked</dfn> |
| instruction sequence. For purposes of aligned instruction bundle mode, a |
| sequence starting with <code>.bundle_lock</code> and ending with |
| <code>.bundle_unlock</code> is treated as a single instruction. That is, the |
| entire sequence must fit into a single bundle and may not span a bundle |
| boundary. If necessary, no-op instructions will be inserted before the |
| first instruction of the sequence so that the whole sequence starts on an |
| aligned bundle boundary. It's an error if the sequence is longer than the |
| bundle size. |
| |
| <p>For convenience when using <code>.bundle_lock</code> and <code>.bundle_unlock</code> |
| inside assembler macros (see <a href="Macro.html#Macro">Macro</a>), bundle-locked sequences may be |
| nested. That is, a second <code>.bundle_lock</code> directive before the next |
| <code>.bundle_unlock</code> directive has no effect except that it must be |
| matched by another closing <code>.bundle_unlock</code> so that there is the |
| same number of <code>.bundle_lock</code> and <code>.bundle_unlock</code> directives. |
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